Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles called soot.
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulates and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as, for example, fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine.
Engine manufacturers have employed exhaust treatment devices called particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap is a filter designed to trap particulate matter. The use of the particulate trap for extended periods of time, however, may enable particulate matter to build up on the filter, thereby causing the functionality of the filter and/or engine performance to decline.
One method of restoring the performance of a particulate trap may be to implement regeneration. Regeneration of a particulate trap filter system may be accomplished by increasing the temperature of the filter and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter and regenerating the filter system.
Engine manufactures have also employed catalytic materials (catalysts) to chemically purify exhaust gases. Catalyst-based treatment devices may include catalysts that promote removal of selected pollutants from an exhaust stream by oxidizing and/or reducing particular gaseous compounds in the exhaust. These may include NOx, carbon monoxide (CO), or any other gaseous compound desired to be removed from the exhaust stream. A catalyst-based treatment device, such as a NOx adsorber, may also be regenerated by simply running the engine with a rich air-fuel mixture.
Temperature can be an important factor with regard to both particulate traps and catalyst-based treatment devices. Particularly, excessive heat from various sources in an exhaust system can cause performance losses and/or mechanical failures of particulate traps and catalyst-based treatment devices. These sources of heat may include the exhaust gas supplied to the exhaust treatment devices, regeneration of the devices, and exothermic reactions. Also, some exhaust treatment devices may not perform at their full potential at temperatures that are too low. For example, regeneration may be best achieved above a particular temperature. Additionally, chemical reactions that take place in catalyst-based treatment devices may also occur most effectively above a particular temperature.
Abnormal operating temperatures may be indicative of problems with the exhaust treatment devices. For example, structural and/or mechanical failures of an exhaust treatment device may alter flow paths of exhaust gases, resulting in increases or decreases in flow through particular sections of an exhaust treatment device. Increases or decreases in flow may result in corresponding increases or decreases in the operating temperature and/or the rate of change of the operating temperature through those particular sections.
By monitoring the temperature of exhaust treatment system components, the exhaust treatment may be controlled to prevent the components from being subjected to destructively high temperatures and/or to maintain the operating temperatures within a desired range. Systems have been proposed for reducing damage caused by heat in exhaust treatment system components. For example, U.S. Pat. No. 6,622,480, issued on Sep. 23, 2003 to Tashiro et al. (“the '480 patent) discloses an exhaust treatment system including a catalytic particulate filter. The '480 patent further discloses closed loop feedback control of regeneration of the particulate filter based on exhaust temperatures measured immediately upstream and downstream of the particulate filter in an attempt to minimize damage to the components that may result from excessive heat.
While the system of the '480 patent may monitor the overall temperature of the particulate filter, the system of the '480 patent has several drawbacks. For example, it does not monitor deviations in temperature at localized portions of the particulate filter. Localized temperature deviations may be indicative of local structural failures in an exhaust treatment device that could possibly result in significant loss of performance and/or more extensive damage to the exhaust treatment device or other components of the engine or exhaust system.
The disclosed exhaust treatment device monitoring system is directed toward overcoming one or more of the problems set forth above.